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- M. L. Dinis and A. Fiúza, “Exposure Assessment to Radionuclides Transfer in Food Chain”, Nato AISI, Minsk.
M. L. Dinis and A. Fiúza, “Modeling the Transfer and Fate of Contaminants in the Environment: Soil, Water and Air”, in Chemicals as Intentional and Accidental Global Environmental Threats, L. Simeonov and E. Chirila Editors, Springer, ISBN-10: 1-4020-5097-6; ISBN-13: 978-1-4020-5097-8; 2006, ISI Web of Knowledge: Times Cited: 1, References: 5The environmental effects originated by uranium mining activities result mainly from the wastes generated by the ore processing. Large quantities of radioactive wastes are generated in this extractive process requiring a safe management. Besides the radioactivity these wastes mar algo hold different amounts of chemicals used in the extraction process, toxic pollutants associated with the mineralization and precipitates provoked by pH or Eh alterations. The main concem of waste management and long term stabilization is to confine the residues in order to reduce the dispersion of contaminants to concentrations that not exC'eed the trigger values considered to be safe: there is thus a need to ensure that the environmental and health risk from these materiaIs are reduced to an acceptable leveI. However, the confinement will always represent a potential source of environmental contamination to the air, soil, superficial water and groundwater, due to the contaminants release and transport in the environment, which mar occur by natural erosion agents like rainfall or wind. 
Generally sites with radioactive contamination are also simultaneously polluted with many other different toxics, especially heavy metals. The environmental effects originated by uranium mining activities result mainly from the wastes generated by the ore processing. Besides the radioactivity these wastes may also hold different amounts of chemicals, toxic pollutants and precipitates originated by pH or Eh alterations. The radionuclides released from these wastes can give rise to human exposure by transport through the atmosphere, aquatic systems or through soil sub-compartments. The exposure may result from direct inhalation of contaminated air or ingestion of contaminated water, or from a less direct pathway - the ingestion of contaminated food products. Nevertheless this pathway can be quite significant as a result of biological concentration in the foodstuff. The exposure resulting from airborne particulates containing 230Th, 226Ra, and 210Pb as well as uranium, is primary by the inhalation of particles and or through the food chain. The predominant target effective dose from these radionuclides is to the bones. Non-radioactive metals and other chemical reagents may also induce chronic or acute health effects. The harmful effects of radionuclides do not come from their chemistry within tissue, but from the radiation associated with radioactive decay which increases the risk of cancer. Contamination of the trophic chain by radionuclides released into the environment can be a component of human exposure to ionizing radiations by transferring the radionuclides into animal products that are components of the human diet. Plants in general tend to accumulate radionuclides in a scale dependent on many factors and within animals and humans, certain tissues tend to accumulate selected radionuclides. Radionuclides deposition can be a significant pathway to human exposure by first ingestion of contaminated pasture by animals and then by the ingestion of animal products contaminated (dairy or meat). The relevant incorporation of the radionuclides in the milk is usually due to the ingestion of contaminated pasture. This transfer process is often called the pasture-cow-milk exposure route. We developed a compartment dynamic model to describe mathematically the radionuclide behavior in the pasture-cow-milk exposure route and predict the activity concentration in each compartment following an initial radionuclide deposition. The dynamic model is defined by a system of linear differential equations with constant coefficients based in a mass balance concept. For each compartment a transient mass balance equation defines the relations between the inner transformations and the input and output fluxes. The fluxes between the compartments are estimated with a transfer rate proportional to the amount of the radionuclide in the compartment. The model also considers possible transformations within the compartment. The first model considered for the propagation through the food chain is relatively simple and classic and considers as initial state a contaminated pasture that is consumed by a cow that produces a certain quantity of milk. A more sophisticated model is also described taking into account the spread of 226Ra within the cow by the inclusion of several sub-compartments: the gastrointestinal system (GIT), the plasma and the bones. For the exploration of the model we defined several radionuclides as relevant but, for the present, only radium was considered in the calculations, due to the availability of data. The endpoints are radium concentrations in the soil, pasture, GIT, plasma, bone and milk. The concentration within each compartment can then be transcribed to doses values on the bases of a simplified exposure pathway and a pre-defined critical group.
Radon exhalation from uranium mining and milling sites can constitute a complex environmental situation and subsequently become a health risk to the population in the vicinity. Post closure and rehabilitation site involves, among other situations, controlling and estimating radon release from the surface pile. Generally the primary cleanup method consists of enclosing the tailings in which the contaminated area is covered with compacted clay or native soil, to prevent the release of radon, and then covered with rocks and vegetation. This implies a cover design and placement which will give long term stability and control to acceptable levels of radon emission, gamma radiation, erosion of the cover and the tailings and infiltration of the precipitation into the tailings. Not only are these situations being prevented with the cover but also the transport of other pollutants from the tailings to the environment and restraining the access of people and animals. Cover design involve estimating the cover thickness assuring a radon flux inferior of the acceptable values. Cover thickness depends on the properties of the materials to apply in the cover and the tailings characteristics. Usually radon flux is estimated with diffusion equations across a porous medium which describes mathematically the radon movement in the tailings and in the cover characterized by the radon diffusion coefficient, porosities, moistures of the tailings and cover, the radium content and the tailings emanation coefficient. Radon exhalation rates are controlled mostly by the amount of radium and the moisture present in the tailings. An algorithm based on the theoretical approach of diffusion was developed to estimate radon attenuation originated by a cover system placed over the tailings pile and subsequently the resulting concentration in the breathing atmosphere. The one dimensional steady-state radon diffusion equation was applied to a porous and multiphase system. Also the thickness of a cover that limits the radon flux to a stipulated value can be performed.
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